ASSAY PROCEDURE AND APPLICATION IN IDENTIFICATION OF HERBICIDES

Abstract: An assay for detecting inhibitors of aminoacyl-tRNA synthetases, which when reacted with divalent metal cations, a corresponding species of tRNA and an appropriate non-cognate amino acids catalyse the hydrolysis of ATP to pyrophosphate; the assay comprising incubating a divalent metal cation, ATP, the said tRNA, the said non-cognate amino acid, inorganic pyrophosphatase and the said aminoacyl-tRNA synthetase, in at least a partially pure form, both with and without a potential inhibitor and providing detecting means for phosphate and comparing the results obtained.

Description: ASSAY PROCEDURE AND APPLICATION IN IDENTIFICATION OF HERBICIDES The present invention relates to a new assay procedure for detecting compounds which inhibit the activity of certain aminoacyl-tRNA synthetases, to the use of these procedures for identifying compounds which have such activity for use as antibiotics or herbicides, to herbicides derived thereby, and to a novel cDNA sequence encoding E^ coli isoleucyl-tRNA synthetase. Aminoacyl-tRNA synthetases are enzymes found in all bacteria, plants and animals and are required to make protein. Inhibitors of the bacterial enzymes are potentially useful as antibiotics and the applicants have discovered that they may also have application as herbicides. It is vital that the genetic code is accurately translated into protein. To ensure that this happens each aminoacyl-tRNA synthetase must attach the right (cognate) amino acid to the right (cognate) species of tRNA. To ensure that this happens, certain of these enzymes have evolved "editing" mechanisms to hydrolyse (at different stages) inappropriate intermediates complexes and "mischarged" tRNA species. Particular examples are valine, a non-cognate amino acid with respect to isoleucyl-tRNA synthetase (hereinafter referred to as ITRS) (1), threonine (2), a non-cognate amino acid with respect to valyl-tRNA synthetase and homocysteine, a non-cognate amino acid with respect to methionyl-tRNA synthetase. The applicants have found a means of using these editing mechanisms to develop an assay technique for discovering inhibitors of enzyme activity and consequently of biologically active compounds having industrial applicability. According to one aspect of the present invention there is provided an assay for detecting inhibitors of an aminoacyl-tRNA synthetase, which when reacted with a divalent metal cation, a corresponding species of tRNA and an appropriate non-cognate amino acid, will result in the hydrolysis of ATP to pyrophosphate; the assay comprising incubating the said divalent metal cation, ATP, the said tRNA, the said non-cognate amino acid, inorganic pyrophosphatase and the said aminoacyl-tRNA synthetase, in at least a partially pure form, both with and without a potential inhibitor and providing detecting means for phosphate and comparing the results obtained. According to another aspect of the present invention there is provided an assay for detecting isoleucyl-tRNA synthetase of E^ coli comprising (a) incubating magnesium ions, adenosine triphosphate (ATP), a corresponding species of tRNA, isoleucyl-tRNA synthetase and inorganic pyrophosphatase with valine; (b) simultaneously incubating a similar mixture further containing a potential inhibitor of the enzyme; (c) detecting phosphate production from the incubates; and (d) comparing the results. As used herein, the expression "partially pure" used in relation to enzyme means that the enzyme preparation is substantially free of interfering activities, in particular is substantially free of phosphatases and, for example, in the particular case of the assay for ITRS exemplified, free of valyl-tRNA synthetase. The tRNA employed in the assay technique may be pure tRNA appropriate for the particular enzyme or a mixture of tRNAs, such as the mixture of tRNA species from E. colistrain W commercially obtainable from Sigma (UK) Ltd, provided that the mixture contains sufficient of the tRNA appropriate for the particular enzyme. The assay of the invention is applicable for the screening of chemicals for biological activity in a commercial environment. Consequently the term "readily hydrolysable" means that the assay reaction can proceed at a useful rate. Particular examples of enzymes and amino acids which can be employed in this screen because of the editing mechanism by which the misacylated products are removed are ITRS, valyl-tRNA synthetase and ethionyl-tRNA synthetase with valine, threonine and ho ocysteine respectively. The divalent metal cation is preferably magnesium or manganese. Magnesium is especially preferred. In a preferred embodiment the enzyme employed in the assay is ITRS from a bacterial source, preferably E. coli. and the amino acid is valine. The assay is based upon the principles exemplified below. The two partial reactions of ITRS (enzyme) involved in the biosynthesis of the aminoacyl-tRNA can be represented as follows: 1) Enzyme (ITRS) + ATP + ile <—> Enzyme:ile-AMP + PPi 2+ ITRS, in the presence of Mg ions catalyses a partial reaction in which pyrophosphate (PPi) is released and an aminoacyl adenylate (ile-AMP) is formed which remains very tightly bound to the enzyme. 2) Enzyme:ile-AMP + tRNA lleu <—> ile-tRNA lle + AMP + Enzyme The enzyme-bound aminoacyl adenylate reacts with the cognate tRNA to transfer the ileu to the tRNA and to release adenosine monophosphate (AMP). As can be seen, pyrophosphate is produced in step 1. Adding inorganic pyrophosphatase converts this to phosphate (which can be measured, for example, colormetrically by a suitable phosphate determination method such as that involving malachite green described by Lanzetta et al (3) and slightly modified by Howard and Ridley (4)). Consequently it should be possible to detect ITRS activity by detecting phosphate. However, the above two reactions are tightly coupled. The stoichiometry requires one equivalent of tRNA to react for each pyrophosphate released. Large amounts of tRNA would be needed to generate enough pyrophosphate and subsequently phosphate to detect. This would be too costly to employ on a routine basis and for use in a high throughout screen. When valine is substituted for isoleucine it also initially reacts to form the aminoacyl AMP bound to the enzyme. The reaction scheme can be represented as follows: 1. Enzyme + ATP + val <—> Enzyme: val-AMP + PPi 2. tRNA lle + Enzyme: val-AMP <—> tRNA lle + Enzyme + val + AMP In this case rather than forming the aminoacyl-tRNA, it is rapidly ile hydrolysed by the ITRS enzyme in the presence of tRNA (5). The assay of the invention makes use of this in that valine allows the tRNA to be recycled so that it does not limit the extent of the reaction. Thus, the enzyme catalyses the hydrolysis of ATP to PPi (and, via pyrophosphatase, ultimately, Pi). Since the enzyme catalyses the hydrolysis of the non-cognate aminoacyl adenylate bound to the enzyme and there is no transfer to the tRNA, only catalytic amounts of tRNA are required. In addition the starting enzyme and valine are also regenerated while generating pyrophosphate. Experiments with the assay conditions have shown that once the reaction with the ITRS enzyme was started, a linear rate could be maintained for at least 40 minutes. A colour change of >0.30D units is preferred. The amount of tRNA which is employed in the reaction is generally low since the tRNA is recycled in the reaction. For example, doses of from about 0.05 mg to about 0.3 mg/200μl reaction mixture may be employed. As discussed above, this may be pure or mixed tRNA species from J . coli. In one preferred embodiment, mixed tRNA species from g coli from Sigma (UK) Ltd is added in an amount of about 0.1mg/200μl reaction mixture. The amount of ATP present can be from about 0.05 to about 10 mM. The Km for valine is about 0.5mM, so at least 0.5mM of valine, suitably from about 0.5mM to about 25 mM of valine, preferably about 5mM valine is used to obtain near maximum rates. In contrast, the Km for He 3 using an H-Ile assay was found to be about 4.3μM. Purified or partially purified enzyme may be prepared by conventional techniques (6) including use of recombinant DNA technology. Using ITRS obtained from E. coli. and partially purified as described below, amounts of from about 0.10 μg to about 5μg are suitably employed. Based on this amount, suitable assay times have been found to be up to about 90 minutes or longer. We have also now sequenced the gene encoding for E... coli ITRS. Thus, according to another aspect of the present invention there is provided a cDNA sequence as shown in Seq ID No 1, including non-critical allelic variations of that sequence. According to yet another aspect of the present invention there is provided an amino acid sequence as shown in Seq ID No 2, including variants thereof having non-critical amino acid substitution(s) or deletion(s) at one or more locations in that sequence. The present invention includes sequences having at least 70% nucleic acid homology with the sequence shown in Seq ID No 1, and which encode for functionally equivalent proteins. In a preferred embodiment, the nucleic acid sequence has at least 75%, 80%, 85%, 90%, 95%, 97% or 99% homology with the sequence shown in Seq ID No 1. The present invention includes functionally equivalent sequences to that shown in Seq ID No 2, having at least 70% homology with said sequence. In a preferred embodiment, the amino acid sequence has at least 75%, 80%, 85%, 90%, 95%, 97% or 99% homology with the sequence shown in ID Seq No 2. It will be appreciated that the expressed ITRS can be used in the assay of the present invention. By using the assay technique described above, it is possible to carry out high throughput screens for detecting inhibitors of the enzymes. In a further aspect of the invention there is provided an enzyme inhibitor having biological application detected by an assay method as described above. In particular the applicants have found that inhibitors of ITRS may have application as herbicides. Such compounds are described in our co-pending International Patent Publication No. W093/19599. In yet a further aspect of the invention there is provided a herbicidal compound which acts by inhibiting the plant isoleucyl-tRNA synthetase enzyme excluding those compounds of International Patent Publication No. W093/19599 of general formula (I) or (IA) or (IB) where Y 2 represents a group of sub-formula (IC) or (ID or (IE) and wherein R is a 3 3 group CO-XR wherein X is 0 or S and R is hydrogen or an agrochemically acceptable ester-forming radical; or R is a group -R wherein R is an 2 optionally substituted aryl or heterocyclic group; or R is a group 5 6 5 6 CO-NR R wherein R and R are the same or different and each represent an agrochemically acceptable amide-forming radical; stereoisomers of the compounds of formula (I), (IA) and (IB) and salts of the compound of formula (I), (IA) and (IB) wherein R 2 is COXR 3 , X is 0 and R 3 is hydrogen. The following examples illustrate the invention. 1. Partial Purification of E. coli ITRS a) Cell breakage: lOOg of E_j. coli cell paste was mixed with 200ml of buffer A (lOOmM Tris (tris(hydroxymethyl)aminomethane) pH7.4, 30mM KCl, 0.5mM MgCl 2 , O.l M EDTA (ethylenedinitrilotetraacetate) , 4mM 2-mercaptoethanol , 6mM DTT (dithiothreitol) and ImM benza idine) . The cells were broken in a French press at 8,000 psi (5.5x10 kPa) . The extract was spun at 23,500 x g (12,000rpm) in a 6 x 250ml Sorvall GSA rotor for 20 minutes at 4°C. b) Precipitation: The supernatant was removed and 2.5% protamine sulphate in buffer A was added in a dropwise manner to a final concentration of 0.1%. The extract was centrifuged at 23,500 x g (12,000 rpm) for 20 minutes. The supernatant was removed, and 50% ammonium sulphate added slowly and left to mix on ice for 30 minutes. The extract was spun again at 12,000 rpm for 15 minutes to form a pellet. c) Gel filtration on a Sephadex G-50 column: The pellet was resuspended in a small amount of buffer B (25mM Tris pH 7.4, 5mM MgCl 2 , ImM EDTA, 4mM 2-mercaptoethanol) . A further spin in a 8 x 50ml Sorvall SS-34 rotor at 39,000 x g (18,000 rpm) for 15 minutes was carried out prior to the extract being added to a Sephadex G-50 column (5cm i.d.) with a bed volume of 250ml. The protein eluted with buffer B was collected and stored at -80°C. d) Ion-exchange on a Q-Sepharose Column: A pre-equilibrated Pharmacia Q-Sepharose column (11.5cm x 5cm) in buffer B was prepared. The extract from the Sephadex G-50 column was added, and a 0 to 1M NaCl gradient applied. All the fractions from this column were kept and analysed by the radiolabelled method described below. The active fractions (47 - 57) were pooled, and had 90% ammonium sulphate added and were then spun at 12,000 x g (17,400 rpm) in the 8 x 50ml Sorvall SS-34 rotor for 15 minutes. The supernatant was removed and the resulting pellet was dissolved in buffer B. e) Gel Filtration on a Superdex-200 Column: Five ml of the extract from step d) was added to a pre-packed Pharmacia Superdex-200 HiLoad column (2cm i.d.) with a bed volume of 120ml. It was pre-equilibrated in buffer B and 50mM NaCl. All of the fractions were kept separate and tested using the radiolabelled assay. Fractions 25 - 40 were pooled and an equal volume of glycerol was added. When this extract was used for the initial development work on the colorimetric assay it was found to contain contaminating phosphatase activity. f) Removal of Contaminating Phosphatase Activity: Using a high resolution Q-Sepharose column with a gradient of 0 - 1M NaCl on an FPLC system, fractions containing ITRS activity free of contaminating phosphatase were eluted at 0.3M NaCl. 3 2. Measurement of ITRS Activity using a H-Isoleucine-Based Radiolabelled Assay The activity of ITRS during fractionation was monitored using conditions based on the method described by Steinmetz and Weil (7), and as described below. Stock reagents used in the method are as follows: Buffer solution: 500mM Tris-HCl pH7.4, 150mM MgCl 2 , 6H 2 0, 300mM KCl, 25mM glutathione, and 1% bovine serum albumin (BSA). ATP: lOmM in 50mM-Tris-HCl pH 7.4. tRNA (mixed): ile Approximately 0.54nmoles tRNA /mg from the J . coli strain W (supplied by Sigma (UK) Ltd). A stock was made of 50mg mixed tRNA/ml 50mM Tris-HCl pH 7.4. Isoleucine: 3 L-[4,5- H]-Isoleucine (obtained from Amersham) at approximately 3 lOOCi/mmole in 2% aqueous ethanol. A lOOμM stock was prepared of 50μl H- isoleucine, lOOμl cold isoleucine, and 850μl 50mM Tris-HCl pH7.4. Enzv e - ITRS: Prepared as described above. The specific activity of the enzyme used in the present example was approximately 145nM of product formed/minute/mg, and was about 5% - 10% active. The enzyme was diluted as appropriate. It will be appreciated that the enzyme amounts in the assay can be adjusted according to the purity of the enzyme used. The assay mixture for a final volume of 200μl was composed of: 20μl buffer solution 20μl ATP 20μl tRNA 3 20μl H-Isoleucine solution lOOμl 50mM Tris-HCl pH 7.4 The standard assay (in 200μl) was carried out in quadruplicate in Eppendorf microcentrifuge tubes. The ingredients were preincubated for 2-3 minutes at 37°C, and the reaction started by addition of approximately 20μl of the appropriately diluted enzyme extract as described above. The final reaction contained reagents in the following concentrations: 50mM Tris-HCl, pH 7.4 15mM MgCl 2 , 6H 2 0 30mM KCl 2.5mM Glutathione 0.1% bovine serum albumin ImM ATP 5mg ml "1 tRNA 3 lOμM Isoleucine containing H-Ile The assay was incubated at 37°C for 20 minutes, and stopped by addition of 50μl 20% TCA, and the tubes placed on ice. 2 200μl of the reaction mixture was pipetted onto 1.5cm cellulose 3MM filters. The filters were washed (in groups of 4) as follows: 1 x 10% TCA, 2 x 5% TCA, and 2 x ethanol using fresh wash medium for each set of replicates to avoid cross contamination. The dried filters were placed in 20ml scintillation vials and the radioactivity counted in 15ml Optiphase. 2. Measurement of ITRS activity using a Colorimetric Assay based on using Valine as Substrate Incubations were set up in quadruplicate (as above) with a final volume of 200μl as described below. Stock reagents used in the method were as follows: Buffer solution: 500mM Tris-HCl pH7.4, 150mM MgCl 2 , 6H 2 0, 300mM KCl, 25mM glutathione, and 1% bovine serum albumin (BSA) . ATP: 7.5mM in 50mM Tris-HCl pH 7.4. tRNA (mixed): ile Approximately 0.54nmoles tRNA /mg from the J . coli strain W (supplied by Sigma (UK) Ltd). A stock was made of 1.2mg mixed tRNA/ml 50mM Tris-HCl pH 7.4. L-Valine A 30mM stock in 50mM Tris-HCl pH 7.4. Inorganic Pyrophosphatase This was in the form of the HPLC purified grade from Bakers yeast supplied by Sigma (UK) Ltd as a lypophilized powder. This was made up in 50mM Tris-HCl pH 7.4 to a concentration of 10 units/ml. Enzyme - ITRS: Prepared as described above. The specific activity of the enzyme used in the present example was approximately 145nM of product formed/minute/mg, and was about 5% - 10% active. The enzyme was diluted as appropriate. It will be appreciated that the enzyme amounts in the assay can be adjusted according to the purity of the enzyme used. The assay mixture for a final volume of 200μl was composed of: 20μl buffer solution 20μl ATP 20μl tRNA 20μl inorganic pyrophosphatase lOOμl L valine The standard assay (in 200μl) was carried out in quadruplicate in Eppendorf microcent ifuge tubes. The ingredients were pre-incubated for 2-3 minutes at 37°C and the reaction started by addition of 20μl of appropriately diluted enzyme extract (as described above). Thus the final reaction contained reagents in the following concentrations: 50mM Tris-HCl pH 7.4 lO M MgCl 2 30mM KCl 2.5mM Glutathione 0.75mM ATP 15mM Valine 0.12mg of mixed tRNA species from J . coli (as described above) HPLC purified from Bakers yeast avilable from by Sigma (UK) Ltd 1 unit/μl of inorganic pyrophosphatase and an appropriate concentration of ITRS (for example 1-2 g/ml of the enzyme as described above). The samples were incubated at 37°C for 20 - 60 minutes. The reaction is stopped by the addition of a Malachite Green containing reagent as described by Howard and Ridley (4) and subsequently quenched with the addition of 34% citric acid. The optical absorbance is then measured at a wavelength of 630nm using a spectrophotometer. The Km value of 0.048mM of ATP was determined using the novel colorimetric assay was in close 3 agreement with the Km of 0.047mM obtained using the H-Ile assay. The inhibition constants of two compounds were measured and the 3 results compared with the values obtained using the standard H-isoleucine assay. Compound 1 was tested at 0, 0.25 μM and 1.0 μM concentrations with 3 varying H-Isoleucine concentrations up to lOOμM, and was seen to be competitive with respect to isoleucine. Results Concentration giving 50% inhibition (I ς n) measured using the valine-based assay of the present invention: Compound 1 Compound 2 I 50 2000nM 38nM Concentration giving 50% inhibition U rn ) measured using the standard H-isoleucine radiometric assay: Compound 1 Compound 2 I 50 109nM 2.3nM The two assays both detected the compounds as inhibitors and both assays indicated that the potencies of the two inhibitors were different. The actual values are different because: 1) Compound 2 is, in reality, more potent than can be measured and the apparent I value is mainly determed by the concentration of enzyme in the assay (8). Since the radiometric assay is more sensitive it uses less enzyme and therefore yields a lower apparent I 50 value than in the assay of the present invention. 2) Both compound 1 and compound 2 are competitive with the amino acid. In the case of the radiometric assay, the amino acid, isoleucine, is used at a concentration only approximately 2 fold above the Km whereas in the assay of the present invention it is some 30 fold greater. Thus, allowing for this fifteen fold difference in the ratio of amino acid concentration to Km, the two values given by the two assays are in good agreement. It will therefore be appreciated that the valine-based assay described here is useful as a colori etric method for detecting inhibitors of E coli ITRS. 3. Sequencing of the E. coli ITRS gene The gene was sequenced in two stages: a) The Promega "Erase-A-Base" kit (Promega Cat. No. E5850) was used. The gene was cloned into the vector pGEM3Zf(-). The Erase-A-Base system allows the contruction of a series of unidirectional nested deletion sets from plasmid or M13 clones using the procedure developed by Henikoff (9). In this case the deletion mutants, each containing a different part of the gene, were sequenced with the pUC/M13 reverse sequence primer (5'-AACAGCTATGACCATG-3') using the Sequenase Version 2.0 kit. b) About 60% of the gene was sequenced using the "Erase-A-Base" system. This sequence information was used to design synthetic oligonucleotide primers (listed below) so that the gaps in the gene sequence could be read. The gaps were filled in and the entire coding nucleotide sequence of the gene obtained. Primers for top strand ITS39F: 5'-GGCATCATCCGTGCGGCT-3' ITS91F: 5'-TATGTGCCTGGCTGGGAC-3' ITS114F: 5'-GGTGAGAAATTCACCGCC-3' ITS226F: 5'-TTTGCCGTAAGCAACGTT-3' ITS346F: 5'-GGTCAGAAATACGGCCTG-3' ITS393F: 5'-CTGCTGCACGTTGAGAAA-3' ITS566F: 5'-CAACACCGCGGCTGGTTC-3' ITS765F: 5'-GCACCAATCCTCTCCTTC-3' ITS808F: 5'-TTCTGGGACGAGCTGTTG-3' Primers for bottom strand ITS252R: 5'-TTGCGCGGTTGGCAGGCA-3' ITS336R: 5'-CGCGGTGTGAACGGCACC-3' ITS526R: 5'-TTTCACGTACTGATCAGC-3' References (1) Fersht et al (1977) Biochemistry, 1£, 1025-1028, (2) Fersht et al (1976) Biochemistry, 15., 3342-3346, (3) Lanzetta et al (1979) Anal. Biochem., 100, 95-97, (4) Howard and Ridley (1990) FEBS. Lett., 251, 261-264, (5) Baldwin, A.N. and Berg, P. (1966) J. Biol. Chem., 241, 839-845 (6) Durekovic, A., Flossdorf, J and Kula, M.R. (1973) Eur. J. Biochem, 3Ji, 528-533, (7) Steinmetz, A. and Weil, J-H. (1986) Methods in Enzymology, 118, 212-231 (8) Henderson (1973) Biochem. J., H , 101-107, (9) Henikoff, S. (1984) Gene, 28, 351 CHEMICAL FORMULAE (IN DESCRIPTION) OH CHEMICAL FORMULAE (IN DESCRIPTION) OH .CH .CH— (IC) XH CH, CH / CH- (ID) ^ HC ^CH, 0 2 SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: (A) NAME: Zeneca limited (B) STREET: 15 Stanhope Gate (C) CITY: London (E) COUNTRY: UK (F) POSTAL CODE (ZIP) : W1Y 6LN (ii) TITLE OF INVENTION: Assay Procedure and Application in Identification of Herbicides (iii) NUMBER OF SEQUENCES: 2 (iv) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentln Release #1.0, Version #1.25 (EPO) (2) INFORMATION FOR SEQ ID NO: 1: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 2820 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: CDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 1..2814 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1: ATG AGT GAC TAT AAA TCA ACC CTG AAT TTG CCG GAA ACA GGG TIC CCG 48 Met Ser Asp Tyr Lys Ser Ttir Leu Asn Leu Pro Glu Thr Gly Phe Pro 1 5 10 15 ATG CGT GGC GAT CTC GCC AAG CGC GAA CCC GGA ATG CTG GCG GGT TGG 96 Met Arg Gly Asp Leu Ala Lys Arg Glu Pro Gly Met Leu Ala Arg Trp 20 25 30 ACT GAT GAT GAT CTG TAC GGC ATC ATC CGT GCG GCT AAA AAA GGC AAA 144 Thr Asp Asp Asp Leu Tyr Gly lie lie Arg Ala Ala Lys Lys Gly Lys 35 40 45 AAA ACC TTC ATT CTG CAT GAT GGC CCT CCT TAT GCG AAT GGC AGC ATT 192 Lys Thr Phe lie Leu His Asp Gly Pro Pro Tyr Ala Asn Gly Ser lie 50 55 60 CAT ATT GGT CAC TGG GTT AAC AAG ATT CTG AAA GAC ATT ATC GTG AAG 240 His He Gly His Ser Val Asn Lys He Leu Lys Asp He He Val Lys 65 70 75 80 TCC AAA GGG CTT TCC GGT TAT GAC TCG CCG TAT GTG CCT GGC TGG GAC 288 Ser Lys Gly Leu Ser Gly Tyr Asp Ser Pro Tyr Val Pro Gly Trp Asp 85 90 95 TGC CAC GGT CTG CCG ATC GAG CTG AAA GTC GAG CAA GAA TAC GGT AAG 336 Cys His Gly Leu Pro He Glu Leu Lys Val Glu Gin Glu Tyr Gly Lys 100 105 110 CCG GGT GAG AAA TTC ACC GCC GCC GAG TTC CGC GCC AAG TGC CGC GAA 384 Pro Gly Glu Lys Phe Thr Ala Ala Glu Phe Arg Ala Lys Cys Arg Glu 115 120 125 TAC GCG GCG ACC CAG GTT GAC GGT CAA CGC AAA GAC TTT ATC CGT CTG 432 Tyr Ala Ala Thr Gin Val Asp Gly Gin Arg Lys Asp Phe He Arg Leu 130 135 140 GGC GTG CTG GGC GAC TGG TOG CAC CCG TAC CTG ACC ATG GAC TTC AAA 480 Gly Val Leu Gly Asp Trp Ser His Pro Tyr Leu Thr Met Asp Phe Lys 145 150 155 160 ACT GAA GCC AAC ATC ATC CGC GCG CTG GGC AAA ATC ATC GGC AAC GGT 528 Thr Glu Ala Asn He He Arg Ala Leu Gly Lys He He Gly Asn Gly 165 170 175 CAC CTG CAC AAA GGC GCG AAG CCA GTT CAC TGG TGC GTT GAC TGC CGT 576 His Leu His Lys Gly Ala Lys Pro Val His Trp Cys Val Asp Cys Arg 180 185 190 TCT GOG CTG GOG GAA GCG GAA GTT GAG TAT TAC GAC AAA ACT TCT CCG 624 Ser Ala Leu Ala Glu Ala Glu Val Glu Tyr Tyr Asp Lys Thr Ser Pro 195 200 205 TCC ATC GAC GTT GCT TTC CAG GCA GTC GAT CAG GAT GCA CTG AAA GCA 672 Ser He Asp Val Ala Phe Gin Ala Val Asp Gin Asp Ala Leu Lys Ala 210 215 220 AAA ITT GCC GTA AGC AAC GTT AAC GGC CCA ATC TGG CTG GTA ATC TGG 720 Lys Phe Ala Val Ser Asn Val Asn Gly Pro He Ser Leu Val He Trp 225 230 235 240 ACC ACC CGC CGT GGA CTC TGC CTG CCA ACC GCG CAA TCT CTA TTG CAC 768 Thr Thr Arg Arg Gly Leu Cys Leu Pro Thr Ala Gin Ser Leu Leu His 245 250 255 CAG ATT TCG ACT ATG CGC TGG TGC CAG ATC GAC GGT CAG GCC GTG ATT 816 Gin He Ser Thr Met Arg Trp Cys Gin He Asp Gly Gin Ala Val He 260 265 270 CTG GCG AAA GAT CTG GTT GAA AGC CTA ATG CAG GGT ATC GGC GTG ACC 864 Leu Ala Lys Asp Leu Val Glu Ser Val Met Gin Arg He Gly Val Thr 275 280 285 GAT TAC ACC ATT CTC GGC ACG GTA AAA GGT GCG GAT GTC GAG CTG CTG 912 Asp Tyr Thr He Leu Gly Thr Val Lys Gly Ala Asp Val Glu Leu Leu 290 295 300 CGC TTT ACC CAT CCG TTT ATG GGC TTC GAC GTT CCG GCA ATC CTC GGC 960 Arg Phe Thr His Pro Phe Met Gly Phe Asp Val Pro Ala He Leu Gly 305 310 315 320 GAT CAC GTT ACC CTG GAT GCG GGT ACC GGT GCC GTT CAC ACC GCG CCT 1008 Asp His Val Thr Leu Asp Ala Gly Thr Gly Ala Val His Thr Ala Pro 325 330 335 GGC CAC GGC CCG GAC GAC TAT GTG ATC GGT CAG AAA TAC GGC CTG GAA 1056 Gly His Gly Pro Asp Asp Tyr Val He Gly Gin Lys Tyr Gly Leu Glu 340 345 350 ACC GCT AAC CCG GTT GGC CCG GAC GGC ACT TAT CTG CCG GGC ACT TAT 1104 Thr Ala Asn Pro Val Gly Pro Asp Gly Thr Tyr Leu Pro Gly Thr Tyr 355 360 365 CCG ACG TTG GAT GGC GTG AAC GTC TTC AAA GCG AAC GAC ATC GTC GTT 1152 Pro Thr Leu Asp Gly Val Asn Val Phe Lys Ala Asn Asp He Val Val 370 375 380 GCG CTG CTG CAG GAA AAA GGC GCT CTG CTG CAC GTT GAG AAA ATG CAG 1200 Ala Leu Leu Gin Glu Lys Gly Ala Leu Leu His Val Glu Lys Met Gin 385 390 395 400 CAC AGC TAT CCG TGC TGC TGG CGT CAC AAA ACG CCG ATC ATC TTC CGC 1248 His Ser Tyr Pro Cys Cys Trp Arg His Lys Thr Pro He He Phe Arg 405 410 415 GCG ACG CCG CAG TGG TTC GTC AGC ATG GAT CAG AAA GGT CTG CGT GCG 1296 Ala Thr Pro Gin Trp Phe Val Ser Met Asp Gin Lys Gly Leu Arg Ala 420 425 430 CAG TCA CTG AAA GAG ATC AAA GGC GTG CAG TGG ATC CCG GAC TGG GGC 1344 Gin Ser Leu Lys Glu He Lys Gly Val Gin Trp He Pro Asp Trp Gly 435 440 445 CAG GCG CGT ATC GAG TCG ATG GTT GCT AAC CGT CCT GAC TGG TGT ATC 1392 Gin Ala Arg He Glu Ser Met Val Ala Asn Arg Pro Asp Trp Cys He 450 455 460 TCC CGT CAG CGC ACC TGG GGT GTA CCG ATG TCA CTG TTC GTG CAC AAA 1440 Ser Arg Gin Arg Thr Trp Gly Val Pro Met Ser Leu Phe Val His Lys 465 470 475 480 GAC ACG GAA GAA CTG CAT CCG CGT ACC CTT GAA CTG ATG GAA GAA GTG 1488 Asp Thr Glu Glu Leu His Pro Arg Thr Leu Glu Leu Met Glu Glu Val 485 490 495 GCA AAA CGC GTT GAA GTC GAT GGC ATC CAG GCG TGG TGG GAT CTC GAT 1536 Ala Lys Arg Val Glu Val Asp Gly He Gin Ala Trp Trp Asp Leu Asp 500 505 510 GCG AAA GAG ATC CTC GGC GAC GAA GCT GAT CAG TAC GTG AAA GTG CCG 1584 Ala Lys Glu He Leu Gly Asp Glu Ala Asp Gin Tyr Val Lys Val Pro 515 520 525 GAC ACA TTG GAT GTA TGG TTT GAC TCC GGA TCT ACC CAC TCT TCT GTT 1632 Asp Thr Leu Asp Val Trp Phe Asp Ser Gly Ser Thr His Ser Ser Val 530 535 540 GTT GAC GTG CCT CCG GAA TTT GCC GGT CAC GCA GCG GAC ATG TAT CTG 1680 Val Asp Val Arg Pro Glu Phe Ala Gly His Ala Ala Asp Met Tyr Leu 545 550 555 560 GAA GGT TCT GAC CAA CAC CGC GGC TGG TTC ATG TCT TCC CTA ATG ATC 1728 Glu Gly Ser Asp Gin His Arg Gly Trp Phe Met Ser Ser Leu Met He 565 570 575 TCC ACC GCG ATG AAG GGT AAA GOG CCG TAT CGT CAG GTA CTG ACC CAC 1776 Ser Thr Ala Met Lys Gly Lys Ala Pro Tyr Arg Gin Val Leu Thr His 580 585 590 GGC TTT ACC GTG GAT GGT CAG GGC CGC AAG ATG TCT AAA TCC ATC GGC 1824 Gly Phe Thr Val Asp Gly Gin Gly Arg Lys Met Ser Lys Ser He Gly 595 600 605 AAT ACC GTT TCG CCG CAG GAT GTG ATG AAC AAA CTG GGC GCG GAT ATT 1872 Asn Thr Val Ser Pro Gin Asp Val Met Asn Lys Leu Gly Ala Asp He 610 615 620 CTG CGT CTG TGG GTG GCA TCA ACC GAC TAC ACC GGT GAA ATG GCC GTT 1920 Leu Arg Leu Trp Val Ala Ser Thr Asp Tyr Thr Gly Glu Met Ala Val 625 630 635 640 TCT GAC GAG ATC CTG AAA CGT GCT GCC GAT AGC TAT CGT CGT ATC CGT 1968 Ser Asp Glu He Leu Lys Arg Ala Ala Asp Ser Tyr Arg Arg He Arg 645 650 655 AAC ACC GCG CGC TTC CTG CTG GCA AAC CTG AAC GGT TTT GAT CCA GCA 2016 Asn Thr Ala Arg Phe Leu Leu Ala Asn Leu Asn Gly Phe Asp Pro Ala 660 665 670 AAA GAT ATG GTG AAA CCG GAA GAG ATG GTG GTA CTG GAT CGC TGG GCC 2064 Lys Asp Met Val Lys Pro Glu Glu Met Val Val Leu Asp Arg Trp Ala 675 680 685 GTA GGT TCT GCG AAA GCG GCA CAG GAA GAC ATC CTC AAG GCG TAC GAA 2112 Val Gly Cys Ala Lys Ala Ala Gin Glu Asp He Leu Lys Ala Tyr Glu 690 695 700 GCA TAC GAT TTT CAC GAA GTG GTA CAG CCT CTG ATG CGC TTC TGC TCC 2160 Ala Tyr Asp Phe His Glu Val Val Gin Arg Leu Met Arg Phe Cys Ser 705 710 715 720 GTT GAG ATG GTT TCC TTC TAC CTC GAC ATC ATC AAA GAC CCT CAG TAC 2208 Val Glu Met Val Ser Phe Tyr Leu Asp He He Lys Asp Arg Gin Tyr 725 730 735 ACC CCA AAG GGG ACA GTG TGG GCG CGT CGT AGC TGC CAG ACT GCG CTA 2256 Thr Pro Lys Arg Thr Val Trp Ala Arg Arg Ser Cys Gin Thr Ala Leu 740 745 750 TAT CAC ATC GCA GAA GCG CTG (CTG CGC TGG ATG GCA CCA ATC CTC TCC 2304 Tyr His He Ala Glu Ala Leu Val Arg Trp Met Ala Pro He Leu Ser 755 760 765 TTC ACC GCT GAT GAA GTG TGG GGC TAC CTG CCG GGC GAA CCT GAA AAA 2352 Phe Thr Ala Asp Glu Val Trp Gly Tyr Leu Pro Gly Glu Arg Glu Lys 770 775 780 TAC GTC TTC ACC GGT GAG TGG TAC GAA GGC CTG TTT GGC CTG GCA GAC 2400 Tyr Val Phe Thr Gly Glu Trp Tyr Glu Gly Leu Phe Gly Leu Ala Asp 785 790 795 800 ACT GAA GCG ATG AAC GAT GCG TTC TGG GAC GAG CTG TTG AAA GTG CGT 2448 Ser Glu Ala Met Asn Asp Ala Phe Trp Asp Glu Leu Leu Lys Val Arg 805 810 815 GGC GAA GTG AAC AAA GTC ATT GAG CAA GGG CCT GCC GAC AAG AAA GTG 2496 Gly Glu Val Asn Lys Val He Glu Gin Ala Arg Ala Asp Lys Lys Val 820 825 830 GGT GGC TCG CTG GAA GCG GCG GTA ACC TTG TAT GCA GAA CCG GAA CTG 2544 Gly Gly Ser Leu Glu Ala Ala Val Thr Leu Tyr Ala Glu Pro Glu Leu 835 840 845 TCG GCG AAA CTG ACC GCG CTG GGC GAT GAA TTA GGA TTT GTC CTG TTG 2592 Ser Ala Lys Leu Thr Ala Leu Gly Asp Glu Leu Arg Phe Val Leu Leu 850 855 860 ACC TCC CGC CGC TAC GTT GCA GAC TAT AAC GAC GCA CCT GCT GAT GCT 2640 Thr Ser Arg Arg Tyr Val Ala Asp Tyr Asn Asp Ala Pro Ala Asp Ala 865 870 875 880 CAG CAG AGC GAA CTA CTC AAA GGG CTG AAA GTC GCG TTG ACT AAA GCC 2688 Gin Gin Ser Glu Val Leu Lys Gly Leu Lys Val Ala Leu Ser Lys Ala 885 890 895 GAA GGT GAG AAG TGC CCA CGC TGC TGG CAC TAC ACC CAG GAT GTC GGC 2736 Glu Gly Glu Lys Cys Pro Arg Cys Trp His Tyr Thr Gin Asp Val Gly 900 905 910 AAG GTG GCG GAA CAC GCA GAA ATC TGC GGC CGC TGT GTC AGC AAC GTC 2784 Lys Val Ala Glu His Ala Glu He Cys Gly Arg Cys Val Ser Asn Val 915 920 925 GCC GGT GAC GGT GAA AAA CCT AAG TTT GCC TGATGA 2820 Ala Gly Asp Gly Glu Lys Arg Lys Phe Ala 930 935 (2) INFORMATION FOR SEQ ID NO: 2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 938 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2: Met Ser Asp Tyr Lys Ser Thr Leu Asn Leu Pro Glu Thr Gly Phe Pro 1 5 10 15 Met Arg Gly Asp Leu Ala Lys Arg Glu Pro Gly Met Leu Ala Arg Trp 20 25 30 Thr Asp Asp Asp Leu Tyr Gly He He Arg Ala Ala Lys Lys Gly Lys 35 40 45 Lys Thr Phe He Leu His Asp Gly Pro Pro Tyr Ala Asn Gly Ser He 50 55 60 His He Gly His Ser Val Asn Lys He Leu Lys Asp He He Val Lys 65 70 75 80 Ser Lys Gly Leu Ser Gly Tyr Asp Ser Pro Tyr Val Pro Gly Trp Asp 85 90 95 Cys His Gly Leu Pro He Glu Leu Lys Val Glu Gin Glu Tyr Gly Lys 100 105 110 Pro Gly Glu Lys Phe Thr Ala Ala Glu Phe Arg Ala Lys Cys Arg Glu 115 120 125 Tyr Ala Ala Thr Gin Val Asp Gly Gin Arg Lys Asp Phe He Arg Leu 130 135 140 Gly Val Leu Gly Asp Trp Ser His Pro Tyr Leu Thr Met Asp Phe Lys 145 150 155 160 Thr Glu Ala Asn He He Arg Ala Leu Gly Lys He He Gly Asn Gly 165 170 175 His Leu His Lys Gly Ala Lys Pro Val His Trp Cys Val Asp Cys Arg 180 185 190 Ser Ala Leu Ala Glu Ala Glu Val Glu Tyr Tyr Asp Lys Thr Ser Pro 195 200 205 Ser He Asp Val Ala Phe Gin Ala Val Asp Gin Asp Ala Leu Lys Ala 210 215 220 Lys Phe Ala Val Ser Asn Val Asn Gly Pro He Ser Leu Val He Trp 225 230 235 240 Thr Thr Arg Arg Gly Leu Cys Leu Pro Thr Ala Gin Ser Leu Leu His 245 250 255 Gin He Ser Thr Met Arg Trp Cys Gin He Asp Gly Gin Ala Val He 260 265 270 Leu Ala Lys Asp Leu Val Glu Ser Val Met Gin Arg He Gly Val Thr 275 280 285 Asp Tyr Thr He Leu Gly Thr Val Lys Gly Ala Asp Val Glu Leu Leu 290 295 300 Arg Phe Thr His Pro Phe Met Gly Phe Asp Val Pro Ala He Leu Gly 305 310 315 320 Asp His Val Thr Leu Asp Ala Gly Thr Gly Ala Val His Thr Ala Pro 325 330 335 Gly His Gly Pro Asp Asp Tyr Val He Gly Gin Lys Tyr Gly Leu Glu 340 345 350 Thr Ala Asn Pro Val Gly Pro Asp Gly Thr Tyr Leu Pro Gly Thr Tyr 355 360 365 Pro Thr Leu Asp Gly Val Asn Val Phe Lys Ala Asn Asp He Val Val 370 375 380 Ala Leu Leu Gin Glu Lys Gly Ala Leu Leu His Val Glu Lys Met Gin 385 390 395 400 His Ser Tyr Pro Cys Cys Trp Arg His Lys Thr Pro He He Phe Arg 405 410 415 Ala Thr Pro Gin Trp Phe Val Ser Met Asp Gin Lys Gly Leu Arg Ala 420 425 430 Gin Ser Leu Lys Glu He Lys Gly Val Gin Trp He Pro Asp Trp Gly 435 440 445 Gin Ala Arg He Glu Ser Met Val Ala Asn Arg Pro Asp Trp Cys lie 450 455 460 Ser Arg Gin Arg Thr Trp Gly Val Pro Met Ser Leu Phe Val His Lys 465 470 475 480 Asp Thr Glu Glu Leu His Pro Arg Thr Leu Glu Leu Met Glu Glu Val 485 490 495 Ala Lys Arg Val Glu Val Asp Gly He Gin Ala Trp Trp Asp Leu Asp 500 505 510 Ala Lys Glu He Leu Gly Asp Glu Ala Asp Gin Tyr Val Lys Val Pro 515 520 525 Asp Thr Leu Asp Val Trp Phe Asp Ser Gly Ser Thr His Ser Ser Val 530 535 540 Val Asp Val Arg Pro Glu Phe Ala Gly His Ala Ala Asp Met Tyr Leu 545 550 555 560 Glu Gly Ser Asp Gin His Arg Gly Trp Phe Met Ser Ser Leu Met He 565 570 575 Ser Thr Ala Met Lys Gly Lys Ala Pro Tyr Arg Gin Val Leu Thr His 580 585 590 Gly Phe Thr Val Asp Gly Gin Gly Arg Lys Met Ser Lys Ser He Gly 595 600 605 Asn Thr Val Ser Pro Gin Asp Val Met Asn Lys Leu Gly Ala Asp He 610 615 620 Leu Arg Leu Trp Val Ala Ser Thr Asp Tyr Thr Gly Glu Met Ala Val 625 630 635 640 Ser Asp Glu He Leu Lys Arg Ala Ala Asp Ser Tyr Arg Arg He Arg 645 650 655 Asn Thr Ala Arg Phe Leu Leu Ala Asn Leu Asn Gly Phe Asp Pro Ala 660 665 670 Lys Asp Met Val Lys Pro Glu Glu Met Val Val Leu Asp Arg Trp Ala 675 680 685 Val Gly Cys Ala Lys Ala Ala Gin Glu Asp He Leu Lys Ala Tyr Glu 690 695 700 Ala Tyr Asp Phe His Glu Val Val Gin Arg Leu Met Arg Phe Cys Ser 705 710 715 720 Val Glu Met Val Ser Phe Tyr Leu Asp He He Lys Asp Arg Gin Tyr 725 730 735 Thr Pro Lys Arg Thr Val Trp Ala Arg Arg Ser Cys Gin Thr Ala Leu 740 745 750 Tyr His He Ala Glu Ala Leu Val Arg Trp Met Ala Pro He Leu Ser 755 760 765 Phe Thr Ala Asp Glu Val Trp Gly Tyr Leu Pro Gly Glu Arg Glu Lys 770 775 780 Tyr Val Phe Thr Gly Glu Trp Tyr Glu Gly Leu Phe Gly Leu Ala Asp 785 790 795 800 Ser Glu Ala Met Asn Asp Ala Phe Trp Asp Glu Leu Leu Lys Val Arg 805 810 815 Gly Glu Val Asn Lys Val He Glu Gin Ala Arg Ala Asp Lys Lys Val 820 825 830 Gly Gly Ser Leu Glu Ala Ala Val Thr Leu Tyr Ala Glu Pro Glu Leu 835 840 845 Ser Ala Lys'Leu Thr Ala Leu Gly Asp Glu Leu Arg Phe Val Leu Leu 850 855 860 Thr Ser Arg Arg Tyr Val Ala Asp Tyr Asn Asp Ala Pro Ala Asp Ala 865 870 875 880 Gin Gin Ser Glu Val Leu Lys Gly Leu Lys Val Ala Leu Ser Lys Ala 885 890 895 Glu Gly Glu Lys Cys Pro Arg Cys Trp His Tyr Thr Gin Asp Val Gly 900 905 910 Lys Val Ala Glu His Ala Glu He Cys Gly Arg Cys Val Ser Asn Val 915 920 925 Ala Gly Asp Gly Glu Lys Arg Lys Phe Ala 930 935

Claims: CLAIMS 1. An assay for detecting an inhibitor of an aminoacyl-tRNA synthetase, which when reacted with a divalent metal cation, a corresponding species of tRNA and an appropriate non-cognate amino acid catalyses the hydrolysis of ATP to pyrophosphate; the assay comprising incubating a divalent metal cation, ATP, the said tRNA, the said non-cognate amino acid, inorganic pyrophosphatase and the said aminoacyl-tRNA synthetase, in at least a partially pure form, both with and without a potential inhibitor, and providing detecting means for phosphate, and comparing the results obtained. 2. An assay according to claim 1 wherein the aminoacyl-tRNA synthetase is isoleucyl-tRNA, valyl-tRNA synthetase or ethionyl-tRNA synthetase, and the corresponding non-cognate amino acid is valine, threonine or homocysteine respectively. 3. An assay for detecting isoleucyl-tRNA synthetase of E. coli comprising (a) incubating magnesium ions, adenosine triphosphate (ATP), an appropriate species of tRNA, isoleucyl-tRNA synthetase and inorganic pyrophosphatase with valine; (b) simultaneously incubating a similar mixture further containing a potential inhibitor of the enzyme; (c) detecting phosphate production from the incubates; and (d) comparing the results. 4. An assay according to any one of claims 1 to 3 wherein phosphate is detected colorimetrically. 5. An assay according to any one of the preceding claims which is operated as a high throughput assay. 6. An enzyme inhibitor identified by the assay of any preceding claim. 7. An inhibitor of tRNA synthetase identified by the assay of any one of claims 1 to 5. 8. A herbicidal compound comprising an inhibitor according to either of claims 6 and 7. 9. A herbicidal compound which acts by inhibiting the plant isoleucyl tRNA synthetase enzyme excluding those compounds of general formula ( I) or ( IA) or ( IB) where Y represents a group of sub-formula (IC) or (ID or (IE) XH XH— ( IC ) CH "CH, 2 3 3 and wherein R is a group CO-XR wherein X is 0 or S and R is 2 hydrogen or an agrochemically acceptable ester-forming radical; or R 4 , 4 is a group -R wherein R is an optionally substituted aryl or heterocyclic group; or R is a group CO-NR R wherein R and R are the same or different and each represent an agrochemically acceptable amide-forming radical; stereoiso ers of the compounds of formula (I), (IA) and (IB) and salts of the compound of formula (I), (IA) and (IB) wherein R 2 is COXR 3 , X is 0 and R 3 is hydrogen. 10. A cDNA sequence as shown in Seq ID No 1, including non-critical variations of that sequence. 11. A cDNA sequence according to claim 10 wherein there is at least 703 homology with the cDNA sequence as shown in Seq ID No 1. 12. An amino acid sequence as shown in Seq ID No 2, including variants thereof having non-critical amino acid substitution(s) or deletion(s) at one or more locations in that sequence. 13. An amino acid sequence according to claim 13 wherein there is at least 70% homology with the amino acid sequence as shown in Seq ID No 2.

Inventors: HAWKES TIMOTHY ROBERT, HAWKES, TIMOTHY, ROBERT
Applicants: HAWKES TIMOTHY ROBERT, ZENECA LTD, HAWKES, TIMOTHY, ROBERT, ZENECA LIMITED
Application year: 1994
Main classification: C12Q1
IPC codes: A01N43, C07D309, C07D407, C12N9, C12N15, C12Q1